Delayed coking is a seventy year old refining technology which converts heavy fuel constituents, sometimes referred to as "resid", into lighter products such as gasoline and diesel stock. In the 70's and 80's external factors converged to accelerate the global trend of a diminishing heavy fuel oil market in favor of lighter gasoline and diesel products. Delayed coking now represents approximately twenty percent of the world's resid upgrading capacity and nearly fifty percent of the U.S. capacity. Most petroleum coke is sold as solid fuel and has a relatively low market value, at least in comparison to oil prices.
The delayed coking process takes approximately eighteen hours to produce coke from the resid or hydrocarbon feedstock. The process is carried out in large coke drums, typically twenty seven to twenty nine feet in diameter and approximately one hundred and thirty feet in height. Temperatures in the coke drum range from approximately nine hundred Fahrenheit to nine hundred and fifty degrees Fahrenheit. A coker site typically consists of two or four vertically mounted coke drums, pumps, decoking valves, control rooms, hoisting equipment and material handling equipment.
The hydrocarbon feedstock is fed from a pipe through the bottom flange of the coke drum. A blind flange is bolted onto the coke drum's upper flange during the delayed coking process. Coke formed inside the coke drum is then removed by drilling with high pressure water fed through jets in a drill head attached to a drill stem which is moved axially inside the coke drum using a derrick and a winch.
Once the coking process is complete and the coke drum has been quenched and cooled, the blind flange, weighing approximately 1000-1200 pounds, must be manually removed (unbolted) using an impact wrench. The blind flange is then hoisted away from the coke drum. A clamshell assembly is then manually positioned over the coke drum and bolted to the upper flange where the blind flange was removed. The clam shell assembly is manually opened for insertion of the drill stem and pilot drill head. Once the drill stem is positioned to cut the coke in the coke drum, the clam shell assembly is closed around the drill stem and locked to prevent escaping vapor and particles during the initial phase of the coke cutting process. Once a pilot hole is drilled axially through the coke in the coke drum, the clamshell assembly is unlocked and the pilot drill head and drill stem are removed. The drill stem is then fitted with the final cutting drill head and inserted in the coke drum for completion of the coke cutting process. During the final cutting process, coke is removed from the coke drum through a bottom flange in the coke drum. The clam shell assembly must be manually opened and closed during the final coke cutting process as described for the initial coke cutting process. Once the final coke cutting process is complete, the clam shell assembly is manually removed from the coke drum and replaced with the blind flange which is bolted onto the upper flange of the coke drum.
The manual removal and replacement of the blind flange with the clamshell assembly during the delayed coking process has traditionally been time consuming and hazardous to operations personnel because of the size and weight of the blind flange and because of the hazardous vapors and pressurized steam that escape from the upper flange of the coke drum during removal of the blind flange.
The deheading operation during the delayed coking process has been replaced in some instances by fully automated devices such as U.S. Pat. No. 5,221,019 to Pechacek, et al. and U.S. Pat. No. 5,785,843 to Antalffy, et al. which address the removal of the bottom head or cover of a coke drum. Although fully automated, such devices are typically more expensive to manufacture and operate, making them cost prohibitive under certain conditions. Additionally, fully automated coke drum deheader devices must comply with American Society of Mechanical Engineering (A.S.M.E.) pressure vessel standards as a result of having to seal the coke drum, during the coking process.
Consequently, there is a need for a device capable of removing the top head of a coke drum that overcomes the foregoing disadvantages of the manual process while avoiding expensive manufacturing and operating costs and having to comply with A.S.M.E. standards.